1. Field of the Invention
The present invention relates to a paper-web holding apparatus for a rotary printing press. The apparatus is adapted to prevent pullback of the paper web which would otherwise be effected by a pullback force which is exerted on the paper web when the rotary printing press is halted. The pullback force is induced by, for example, the weight of the paper web or a return movement of a floating roller, which moves against tension of the paper web traveling with a predetermined force imposed thereon.
2. Description of the Related Art
A rotary printing press prints on a paper web which is fed from a paper web feeding unit having a paper roll. When the rotary printing press is not engaged in printing, a printing cylinder is usually separated from THE paper web, so that the paper web traveling through the press unit receives no resistance from the printing cylinder.
Conventionally, a paper-web holding apparatus has been used for retaining a paper web on a roller that guides the paper web, in order to prevent pullback of the paper web when a rotary printing press is halted for any reason. The pullback of the paper web would otherwise be effected in the direction opposite the traveling direction of the paper web by the weight of the paper web or a return movement of a floating roller. Such a conventional paper-web holding apparatus is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. H10-264354.
The paper-web holding apparatus disclosed in the publication is provided in a rotary printing press somewhere between a press unit and a folding unit. When a paper web traveling along a freely rotatable guide roller breaks or gives rise to an abrupt drop in tension thereof with a resultant emergency stop of the rotary printing press, a retaining elementxe2x80x94which includes flexible bristlesxe2x80x94of the apparatus is temporarily activated so as to press the paper web against the surface of the guide roller, thereby preventing the paper web from slipping off or moving in the direction opposite the original traveling direction thereof.
When a traveling paper web breaks or gives rise to an abrupt drop in tension thereof, the printing cylinder separates from the paper web to stop printing, and the rotary printing press makes an emergency stop. After the emergency stop, the guide roller inertially rotates for a while. If the guide roller has a paper-web holding apparatus, a retaining element of the apparatus is activated to elastically press the paper web against the surface of the inertially rotating guide roller by means of tips of bristles thereof.
A frictional force is generated between the inertially rotating guide roller and the paper web which is pressed against the guide roller. This frictional force functions to feed the paper web downstream, thereby tensing the paper web extending upstream from the guide roller.
That is, in the event of an emergency stop, a drive unit for the retaining element is activated to pivotally move the bristles of the retaining element, whereby the paper web in contact with the guide roller is elastically pressed against the surface of the roller by means of the tips of the bristles.
However, the above-described apparatus disclosed in Japanese Patent Application Laid-Open No. H10-264354 involves the following problem. In the event of an emergency stop of the rotary printing press, each guide roller inertially rotates for a while and then stops. At this time, the weight of a paper web which has been released from the restraint of a printing cylinder or a force associated with a return movement of a floating roller of a paper web feeding unit is exerted on the guide roller via the paper web and causes the guide roller to rotate in reverse. As a result, if the paper web is not broken, the paper web is slacked and thus may be wrinkled when printing resumes. If the paper web is broken, the paper web may slip off the guide roller, resulting in consumption of much labor and time for remedial actions to resume printing.
In the field of newspaper printing, with tendencies toward higher printing speed and functional diversification, a so-called shaftless rotary printing press has recently been becoming dominant. The shaftless rotary printing press employs distributed drive units that operate individually. In the shaftless rotary printing press, shafting among the drive units is absent, and each drive unit has a small power source for driving a corresponding drive system, so that rotary elements of each drive unit rotate very lightly. Therefore, when the shaftless rotary printing press is in a halt status, pulling back of a paper web that extends along a travel path may cause rotations of guide rollers, drag rollers for forcibly feeding the paper web, and folding cylinders.
In the shaftless rotary printing press in a halt status, drag rollers for forcibly feeding a paper web, along with other rotary members, may be caused to rotate by the above-mentioned force, thereby potentially raising a problem. Specifically, after the shaftless rotary printing press completes its regular operation and stops normally, drag rollers which are located above formers at an upper section of a folding unit and against which a paper web is pressed at all times by means of propeller rollers may become unable to withstand a force which is exerted thereon via the paper web by the weight of a vertically extending portion of the paper web or by pullback of the paper web which is effected by a return movement of a floating roller in a paper feeding unit, whereby the drag roller may be rotated in reverse, with a resultant pullback of the paper web in the upstream direction.
As a result, a paper web whose leading end has reached the folding unit and which is retained on a folding cylinder by means of pins which serve as retaining means and are stuck into the leading end is pulled back in the upstream direction, and thus may be torn off the pins. If printing resumes in this state, the paper web does not move following rotation of the folding cylinder, and thus a paper jam arises in the folding unit. Therefore, setup work preliminary to resumption of printing must be performed so as to avoid possible occurrence of this paper jam problem, thereby involving relevant consumption of labor and time.
In multi-page printing involving superposition of a plurality of paper webs, the plurality of paper webs are retained in layers on the folding cylinder by means of pins which serve as retaining means and are stuck into the leading ends of the paper webs. In some cases, pullback forces exerted on the paper webs act on the folding cylinder simultaneously via the paper webs to thereby rotate the folding cylinder in reverse. Such reverse rotation of the folding cylinder causes a phase difference between the printing cylinder and the folding cylinder, thereby yielding, after resumption of printing, a lot of printing which suffers misalignment between a printed image and a cutting line. Also, at a certain angle of reverse rotation of the folding cylinder, the leading ends of the paper webs may come off the pins. Therefore, setup work preliminary to resumption of printing must be performed so as to avoid possible occurrence of the above-mentioned paper jam problem, thereby involving relevant consumption of labor and time.
In order to solve the above-mentioned problems, a paper-web holding apparatus must be employed. However, as is easily understood, the aforementioned conventional paper-web holding apparatusxe2x80x94which employs bristles for elastically pressing a paper web against the surface of a guide roller to thereby retain the paper web on the rollerxe2x80x94fails to solve the problem.
An object of the present invention is to solve the above-mentioned problems in the conventional paper-web holding apparatus in a rotary printing press, and to provide a paper-web holding apparatus for a rotary printing press which can reliably hold a paper web on a selected roller, in the event of an emergency stop of the rotary printing press caused by fracture of a paper web or abrupt drop in tension of a paper web during the course of printing or in the event of a normal stop of the rotary printing press after completion of regular printing, to thereby prevent slack of the paper web, slippage of the paper web from the roller, detachment of the paper web from pins of a folding cylinder, and the like, thereby reducing labor and work time involved in startup of the rotary printing press.
To achieve the above object, the prevent invention provides a paper-web holding apparatus for a rotary printing press having rollers which form a path for a paper web fed from a paper web feeding unit to travel along to a folding unit via a press unit and around which the paper web is wrapped. The apparatus comprises a rotation restraint mechanism provided for at least one selected roller and adapted to restrain rotation of the roller when the rotary printing press is halted, and to allow rotation of the roller when the rotary printing press is operated; and a paper presser mechanism provided for the selected roller and having a pressing member which is retreatably advanced toward the roller in order to apply pressing force to the roller at least when the rotary printing press is in a halt state.
The rotation restraint mechanism comprises a hydraulically or magnetoelectrically operable brake unit provided in the vicinity of an end portion of the roller, and a control unit for controlling operation of the brake unit.
The paper-web holding apparatus may be provided for any of guide rollers and drag rollers, including a drag roller located above and upstream of a former for feeding a paper web to the folding unit, or may be provided for each of rollers selected appropriately therefrom.
When the rotary printing press is halted, rotation of at least one roller appropriately selected from drag rollers and guide rollers which form a web path extending to a folding unit via a press unit is restrained. Further, by means of the paper presser mechanism provided for the selected roller, a paper web is pressed against the selected roller whose rotation is restrained. Therefore, the roller is not rotated by gravity or tension imposed on the paper web, and the paper web does not slip on the surface of the roller; i.e., the paper web remains unmoved.